Physics Self-Test - Page 3
17- One Farad is the same as
- (a) one joule/volt
- (b) one Coulomb/volt
- (c) one joule/Coulomb
- (d) one Coulomb/joule
Explanation: Capacitance formula is C = Q / V, so 1 Farad = 1 Coulomb / 1 Volt.
18- If the relative permittivity of the medium increases, the electrical intensity at a point due to a given charge
- (a) Remains constant
- (b) Increases
- (c) Decreases
19- Capacitor is a device used to
- (a) dissipate energy
- (b) store magnetic energy
- (c) vary the resistance
- (d) store electrical energy
20- If a parallel plate capacitor of plate area 2m² and plate separation 1m store the charge of 1.77x10»¹¹ C. What is the voltage across the capacitor?
- (a) 1 V
- (b) 2V
- (c) 3V
- (d) 4V
Explanation:
C = ε₀ · A / d = (8.85×10»¹² · 2) / 1 = 1.77×10»¹¹ F.
V = Q / C = 1.77×10»¹¹ C / 1.77×10»¹¹ F = 1 V.
21- Like charges .......each other, while unlike charges.......each other
- (a) Attract-repel
- (b) Repel-attract
- (c) Don't affect
22- If the relative permittivity of the medium increases, the electrical intensity at a point due to a given charge
- (a) Remains constant
- (b) Increases
- (c) Decreases
23- A parallel plate capacitor has a capacitance C. The area of the plates is doubled and the distance between the plates is halved. What is the new capacitance?
- a) C/4
- b) C/2
- c) 2C
- d) 4C
Explanation: C' = ε₀ · (2A) / (d/2) = 4 · (ε₀A/d) = 4C.
24- Is it possible to have a zero electric field value between a negative and positive charge along the line joining the two charges?
- a) Yes, if the two charges are equal in magnitude.
- b) Yes, regardless of the magnitude of the two charges.
- c) No, a zero electric field cannot exist between the two charges.
- d) Cannot be determined without knowing the separation between the two charges.
Explanation: Between a positive and negative charge, the electric field vectors from both charges point in the same direction (away from positive, toward negative), so they add up and can never cancel out to zero.
25- A point charge is surrounded by a spherical Gaussian surface of radius r. If the sphere is replaced by a cube of side r, will the electric flux be .......
- a. Larger.
- b. Smaller.
- c. The same.
- d. None of the above
Explanation: According to Gauss's Law, the total net electric flux through any closed surface depends only on the enclosed net charge, not the shape or size of the surface.
26- A +3.0 C charge is at the origin and a +9.0 C charge is at x = 4.0 m. Where on the x-axis can a third charge be placed so the net force on it is zero?
- a) x = 2.4 m
- b) x = 1.5 m
- c) x = 0.6 m
- d) x = 0.5 m
27- If the distance between two closely spaced parallel plates is halved, the electric field between the
- a) Is also halved.
- b) Become 4 times as large.
- c) Is doubled
- d) Remains the same.
Explanation: For an isolated parallel plate capacitor setup, the electric field is E = σ / ε₀, which depends only on charge density and is independent of plate separation distance.
28- As per Gauss law ∮ E · ds = qin/ε₀. Which of the following is true about this?
- (a) This is valid for symmetrical surface only
- (b) E is the electric field to the charge inside the surface
- (c) Electric flux on the closed surface due to outside charge is always zero
- (d) Radial, Inward